Of course it helps to have a somewhat clean engine to start with but I always do a good cleaning followed by the protectant that makes it look like new and easier to keep clean in the future.
It also makes it extremely easy to spot a leak of any kind down the road when it's spotless to start with. Not to mention making any future maintenance and repairs possible without turning black from head to toe.
First, make sure you're cleaning a cool motor to avoid possibly cracking it from spraying water or engine cleaner on a hot motor. Take care not to spray directly on electrical components like the coils tho everything is pretty much water tight. I also never spray with force. I've found using the spot free rinse at the car wash to work great.
After spraying everything liberally with the cleaner, I use Gunk, I use several different sized brushes and rags to make sure I've got everything loosened up enough to rinse right off.
Take the time to dry everything off as best you can, such as electrical connections, etc. and drive home.
I might wait a day or 2 til it's dried out good, then spray the protectant liberally all over everything and let it drip dry.
Go back with a clean rag or 2 and wipe up any excess standing puddles.
It can be tedious in places but the end result is a like new looking engine and compartment.
You will smell it for a week or 2 while the warm motor completely dries it.
Better than a used car dealership!
I should add that either prior to or right after cleaning, I pull every electrical connection (sensors etc.) Check for corrosion and apply dielectric grease. Clean the MAF, TPS, etc. Check and replace plugs/wires if necessary using the dielectric grease on them as well.
